The present invention relates to a method of preventing the build-up of static electricity in laminated cork floor-tiles comprising a layer of granular cork bonded by a binder and a wear surface provided on one side of the granular layer. The invention also relates to an anti-static cork floor-tile.
Laminated cork floor-tiles of the above-mentioned type are fitted together to form flooring which, in comparison with other types of flooring, has high elasticity and yields comfortably when walked upon. Such flooring is therefore particularly suitable for use in working environments where personnel have to walk about a good deal since the use of such flooring avoids the strain and stress on legs and back caused by the rigidity of other types of flooring materials. Flooring composed of cork tiles is also aesthetically attractive and provides good thermal insulation.
However, laminated cork tiles used hitherto have the drawback of having low electrical conductivity, causing people and apparatus to become charged with static electricity. It has therefore been impossible to use these tiles in environments in which the build-up of static electricity must be avoided. Such environments are, for example, rooms where explosives or inflammable substances are handled and where a spark might have disastrous results, or premises containing sensitive electronic apparatus such as computer equipment. Until now it has been necessary to use, in such environments, unyielding flooring of, for instance, PVC, the electrical conductivity of which has been increased by various additives. The lower surface of such flooring has been connected to earth at various points.
Attempts have previously been made to increase the conductivity in the wear surface of the work tiles of the type referred to above, which wear surface normally consists of transparent PVC. However, this measure is insufficient to prevent the build-up of static electricity since the electrical charge must be conducted over long distances along the thin wear surface parallel to the floor, across joints creating resistance to the passage of electricity and the overall electrical resistance is therefore too high despite the increased conductivity of the wear surface. It is also possible to reduce resistance to a certain extent by permitting the PVC-based wear surface to cover the edges of the tile and by using a PVC layer on the lower side of the tile as a moisture barrier, this layer, like the layer forming the wear surface and the layer covering the edges also including resistance-reducing additives. The charge will therefore be conducted between the joints, down to the moisture barrier and on to earth. However, not even this measure is sufficient since the combined cross section of the joints is insufficient to conduct the static electricity away. Furthermore, an extra manufacturing stage would be required, entailing added expense, to coat the side edges of the tiles with a layer of PVC once they had been cut to shape.